The thousands of Bristol office workers, students and shoppers who spend the summer months soaking up the sun in Castle Park may have to rethink their plans this year.

Large swathes of the park, which is often described as the green lungs of the city, have been left a sticky brown mess following last weekend's Love Saves The Day festival. And a campaign group has criticised the decision to hand over the public space for more than a week to the organisers, dubbing it 'The Siege of Castle Park'.

Security fencing went up last week and the park, which has been closed to the public since Thursday evening is not due to reopen until Friday morning. Security patrols also kept people away from the park for most of the weekend. Almost all of the main grassed areas have been turned into sticky mud by the combination of more than 20,000 revellers and hours of heavy rain over the weekend.

The festival got underway on Saturday but people who attended spent most of the day sheltering from the heavy rain. The second day of the event saw much brighter weather but the damage had already been done and most of the park had been churned up by early Sunday. Festival-goers in wellies tramped through the city centre and much of the green areas of the park disappeared as they were trampled underfoot.

Joe Spokes, pictured above, 70, moved into the Keg Store flats, on the opposite bank of the Floating Harbour just over five years ago.

He said: "This is the third time the festival has been held in the park. In the past we have put up with all the crowds and the noise. We have also put up with the fact that the park has been closed for more than a week. We were not that upset by that but we are upset by the state of the park this time. From what we can see large areas will not be able to be used this summer."

An online petition has been launched opposing the city council's decision to rent out Castle Park for a private event and the Living Heart group has also complained. The group, whose members include walking and cycling groups, has criticised the closure and called for the policy to be reviewed for next year.

Spokesman Steve Melia said: "Castle Park has been sealed off for a whole week. The heavily used footpath and cycle route from Bristol Bridge to Old Market has been closed with diversions onto busy roads including Newgate, Wine Street and Victoria Street. The organisers of other events like the Harbour Festival and Pride manage to stage music festivals without closing routes for pedestrians and cyclists."

He added: "Parks should be for everyone. To close a park for a week for something lasting two days is ridiculous. For anyone trying to walk from Temple Meads to Broadmead, for example, this puts in a really big detour.

"If the organisers of this event need this sort of military-style security, the council should not allow them to sever vital routes for pedestrians and cyclists. A better arrangement or a different location must be found for next year."

Martin Tweddell, of the Bristol Cycling Campaign, said: "This is blocking a vital part of the National Cycle Network. It is a long way round on busy main roads. In a cycling city where we're supposed to be encouraging people to cycle to take away a vital link like this is appalling."

An online petition has also been launched calling for the park to be kept open for the public.

The petition reads: "Following the complete closure of Castle Park for the third year running, we propose that public parks should never be fenced off in their entirety for commercial events. Tens of thousands of people attending a music event can negatively affect local residents and will inevitably cause damage to this small park.

"Damage takes time and money to repair. A park should be available for public use at all times and even more so during school or bank holidays. We request that Bristol City Council only license commercial events to be held at more suitable venues."

A spokesman for Bristol City Council said: "Love Saves the Day is a very popular event which has been well-attended in the past few years without any significant damage. Unfortunately, this year's weather combined with the number of people attending resulted in areas of the park becoming churned up. We have taken on extra staff to clear, as a matter of urgency, footpaths that were left muddy, and we will carry out work to restore the grass.

"We will re-turf some areas – which means they will have to be fenced off for up to two weeks – while the rest, because of the cost, will need to be re-seeded. Areas which have been re-seeded will need to be fenced off for four to six weeks. This will not cost the council as we will use a combination of the bond provided by the event organisers and some of the licence fee to pay for the restoration work. Clearly, it is unfortunate that bad weather over the weekend resulted in damage and that areas of Castle Green will not be accessible for some weeks.

"We are looking to see what, if any, interim measures could be put in place to enable people to continue to enjoy this very popular open space in the meantime.

"However, events like Love Saves the Day bring a lot of people into the city centre, generating business and helping promote Bristol as a major attraction. We would not want to send out a message that Bristol is not open for business.

"What we will do is sit down and review arrangements for events such as this and see what we could do to minimise damage in the future to keep any disruption as low as possible."